Industrial lift truck



Jan. 8, 1952 w, GlLMAN 2,581,791

INDUSTRIAL LIFT TRUCK Filed June 18, 1949 4 Sheets-Sheet l :E 23 40 45 FIG. I. 29

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ATTORNEYS Jan. 8, 1952 w. M. GILMAN 2,581,791

INDUSTRIAL LIF T TRUCK FIG 2.

V INVENTOR ATTORNEY? 4 Sheets-Sheet 3 INVENTOR WM 7% 52am BY {M W. M. GILMAN INDUSTRIAL LIFT TRUCK ESE] 1 I. 52.

Jan. 8, 1952 Filed June 18, 1949 7m W WM 7 ATTORNEYS Jan. 8, 1952 w. M. GILMAN 2,581,791

INDUSTRIAL LIFT TRUCK Filed June 18, 1949 4 Sheets-Sheet 4 FIG. IO. 26

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' PUMP MTAXI'TORNEYS The outer frame or main portion 2| of the mast also has a ram, or preferably as shown in the present drawings, a pair of rams which are disposed symmetrically in the same transverse plane move concurrently with and at the same speed as said movable member. One way of bringing this about is to support the inner frame directly on said movable member or'members' as by attaching a cross-piece 33 to the upper end of the inner frame or mast extension 22 and securing the upper ends of the two movable members of said pair of rams directly to said cross-piece.

As shown in the drawings; the members of said pair'of rams which are secured to said crosspiece in the present embodiment of the invention are the plungers 34 and 34', their other members, namely, their cylinders 35 and 35' being fastened to the outer frame or main portion 2| of the mast. Where a pair of rams, such as 35 and 35, mounted on .the outer frame or main portion 2| of the mast are used in lieu of a single ram so mounted, the hydraulic system may be referred to as a three-ram system to distinguish from a two-ram system which would be the case if a single ram replaced the pair 35 and 35' aforesaid. And for a purpose which will appear hereinafter in describing the operating sequence of the respective rams while lifting the carrier and inner frame, the sum of the cross-section areas of the pistons of the pair of rams 35, 35' (or if a single ram be substituted therefor, the cross-s ction area of its piston) should be less than the cross-section area of the piston of ram 21, and preferably substantially equal'to one-half the cross-section area of the piston of ram 21. I I

Irrespective of whether the invention be embodied in a two-ram system or in a three-ram system, the cylinders of all the rams in the system are included in and constitute a part of the hydraulic pressure line having means, such as a pump 36, at one end of said line, to cause fluid to flow from a reservoir 31 on the truck body to the ram, or pair of rams as the case may be, mounted on the outer frame 2 and thence to the ram 21 carried by the inner frame 22, said'ram 21 thus constituting the other end of the pressure 1 line. to control the flow of the fluid aforesaid, are installed in a pipe-connection 39 leading, as

The pump and means, such as a va ve 38 shown in the present embodiment of the 'invention, from the reservoir to the respective cylinders of the pair of rams 35 and 35'.

In accordance with the present invention, the plungers 34 and 34' of said pair of rams are hollow and their interior spaces communicate with their respective cylinders on the one hand and on the other hand with the cylinder of the With the pressure line thus constituted,

j pipe connection 4t, 40','and the cylinder of the ram 21.

the hydraulic connection between the pair of rams 35, 35' and the ram 21, that is, the pipe connection 40, 40', may be a rigid connection notwithstanding that the ram 21 must be capable of movement relative to said pair of rams; and this is of considerable advantage since it permits the use of inflexible pipe for the connection 40, 46' as distinguished from flexible hose which, under the constant fiexingand wear and tear to which it is subject in lift trucks of this type, rapidly deteriorates if indeed the internal pressure to which it is also subject does not actually cause it to rupture. Thus, the possibility of using inflexible rather than flexible hose substantially reduces the expense of servicing such trucks.

The control valve 38 may be and preferably is a three-way valve of the open-center type and is provided with three external pipe-connections, to wit: connection 39 to the discharge end of the pump, a connection 4| to the respective cylinders of rams 35, 35', and a connection 42 to the reservoir 31. And said valve has three operative positions controlled respectively by a lever 43 which ma be pivoted on the truck body in a location readily accessible to the operator. When this lever is in the position denoted Lift in the drawings, the control valve will be in a position to connect the discharge end of the pump with the respective cylinders of the rams 35, through the connection 39' and the connection 4|; and when in'this position the control valve will block off the connection 42 to the reservoir. When said lever is in the position denoted Hold" in the drawings, the control valve will be in position to connect the discharge end of the pump with the reservoir through the connection 39' and the connection 42; and when in this position the control valve will block off the connection 4| to the cylinders of the rams 35, 35. -When said lever is in the position denoted Lower in the drawings, the control valve will be in position to connect the cylinders of the rams 35, 35'

with the reservoir through the connection 4| and the connection 42; and when the controlvalve is in this position, it is immaterial whether or not it blocks off the connection 39 to the pump, for

in either case, though the pump continues to operate, it will merely draw fluid from the reservoir and return it directly thereto either through the control valve itself or through a relief-valve 44 installed in a pipe 45 connecting the discharge end of the pump directly to the reservoir. Said relief-valve will also serve as a safety device since it may be adjusted to come into operation whenever the load on the carrier exceeds the capacity for which the apparatus was designed tooperate with safety.

It will of course be understood that a motor (not shown) is provided to drive the pump and, if the truck is of the power-propelled type, that a motor (not shown) will also be provided for its propulsion, together with driving and steering mechanism (not shown) mounted on the truck body so that the operator, either standing, or sitting in the truck, can maneuver the latter from place to place for loading and discharging the load. Moreover, the operator may obtain a clear view ahead for steering, by lowering the inner frame 22 either when the truck is loaded or when free of load; for this will leave a free space between the side 'members of the outer frame ZH, as shown in Fig. 1. And since the frame members 2! and 22 of the mast are disposed in the same transverse plane, the fore and aft dimension of the space needed for installa-' tion of the mast on the truck body will be small, thus tending to reduce the over-all length'of the ram and thus permit the carrier to reach its lowermost position.

Irclaim as my invention: I

1. In a hydraulic lift-truck, the combination of a mast comprising a main portion and a vertically extendible portion, a load-carrier operatively connected to the extendible portion, a hydraulic ram to elevate the carrier upon the extendible portion, a second hydraulic ram to raise the extendible portion upon the main portion of the mast, said second ram having a hollow plunger communicating with both its own cylinder and the cylinder of the first named ram, a fluid reservoir, means to cause fluid to flow from the reservoir to the cylinder of said second ram, and means to check the elevation of the loadcarrier relative to the extendible portion of the mast Without checking the flow of fluid to the cylinder of said second ram.

2. The combination set forth in claim 1 and further characterized by this: that the means to cause fluid to flow from the reservoir to the cylinder of said second ram comprises a pump and that the means to control said flow offluid comprises a valve.

3. The combination set forth in claim 1 and further characterized by this: that the cylinder of the first named ram is fastened to the extendible portion of the mast, that the plunger of the first named ram is operatively connected to the carrier, that the cylinder of said second ram is fastened to the main portion of the mast, and that the plunger of the second named ram is secured directly to the extendible portion of the mast. V

4. In a hydraulic lift-truck, the combination of a mast comprising a main portion and a vertically extendible portion, a load-carrier operatively connected to the extendible portion, a hydraulic ram to elevate the carrier upon the extendible portion, a pair of hydraulic rams to raise the extendible portion upon the main portion of the mast, each ram of saidpair having a hollow plunger communicating with its own cylinder and the cylinder of the first named ram, a fluid reservoir, a pump to cause fluid to flow from the reservoir to the respective cylinders of the rams of said pair, and means to check the elevation of the load-carrier relative to the extendible portion of the mast without checking the flow of fluid to the cylinders of said pair of rams.

5. In a hydraulic lift-truck, the combination of a mast provided with a vertically extendible portion, a load-carrier movable on said extendible portion, a hydraulic ram one member of which is fastened to said extendible portion and the other member operatively connected to said carrier, a second hydraulic ram provided with a holto check the flow of fluid to said second ram in-' dependently of said control valve.

6. In a hydraulic lift-truck, the combination of a'mast provided with a vertically extendible portion, a load-carrier movable on said extendib-le portion, a hydraulic ram one member of which islfastened tolsaid extendible portion and the other member operatively connected to said car- 7 V rier, a second hydraulic ramhaving a hollow plunger which communicates with both its own cylinder and the cylinder of the first named ram,

and said second ram having its said cylinder fas- I tened to said mast and its said plunger in operative relation to the extendible portion of said mast, a fluid reservoir, a pipe-connection between said reservoir and the cylinder of saidlsecond of a mast provided with a vertically extendible portion, a load-carrier movable on said extendible portion, a hydraulic ram one member of which is fastened to said extendible portion and, a

the other member operatively connected to said carrier, a pair of hydraulic rams each having a hollow plunger which communicates with its cylinder and with the cylinder of the first named ram, and each of said pair of rams having one of its members fastened to said mast and its other member secured directly to the extendible portion of said mast, a fluid reservoir, a pipe-connection between said reservoir and the cylinder of each ram of said pair, a pump and a control valve in said connection, an inflexible pipe-connection from the cylinder of the first named ram to each of the hollow plungers of said pair of rams, and means to check the flow of fluid to said 1 pair of rams independently of said control valve.

8. A hydraulic lift-truck comprising, in combination, a' truck body, a mast thereon comprising a main portion secured to the truck body and an extension movable upon the main por tion, a load-carrier movable on the extension, a fluid reservoir, a pressure line including means to cause and means to control the flow of fluid thereto from the reservoir, a hydraulic ram in said pressure line one member of which ram is directly on the extension of said mast, and one I of the members of said second hydraulic ram consisting of a hollow plunger communicating with both its own cylinder and the cylinder of the first named ram.

9. A hydraulic lift-truck comprising a truck body, a mast having a main portion and an ex-- tension movable longitudinally on the main portion, a load-carrier movable longitudinally on said extension, a ram carried by and movable with said extension and the plunger of which is operatively related to the load-carrier to lift the latter on said extension, a second ram supported on the main portion of said mast and the plunger of which is operatively related to said extension to elevate the latter on the main portion of said mast, a reservoir, a conduit connecting the reservoir with the cylinder of said second ram, and a conduit connecting said cylinder with the cylinder of the other ram, and characterized by this: that the main portion of said mast is longitudinall'y immovable on the truck body, the reservoir fixed to said body, and the cylinder of said second ram fixed to the main portion of said mast so that the relative positions of the reservoir and the cylinder of said second ram remain fixed, whereby the conduit connecting the cylinder of said second ram with the reservoir may be a rigid rather than a flexible connection.

10. The hydraulic lift defined in claim 9 flirther characterized by this: that the conduit connecting said cylinders passes through the plunger of said second ram, and that the extension of said mast, the cylinder of the first named ram, and the plunger of said second ram are rigidly connected so as to move together as a single integrated unit.

11. A hydraulic lift-truck comprising a body, a mast having a main portion longitudinally immovable on said body and an extension longi tudinally movable on said main portion, a loadcarrier longitudinally movable on said extension,

a ram the cylinder of which is fast to said extension and the plunger of which is operatively related to said load-carrier to raise the latter on said extension, a second ram the cylinder of which is fast on the main portion of said mast and the plunger of which is hollow and operatively related to said extension to elevate the latter on said main portion, a reservoir fixed: to said body, a rigid conduit connecting the reservoir with the cylinder of said second ram, and a rigid conduit connecting the hollow plunger of said second ram with the cylinder of the other ram.

12. The hydraulic lift-truck defined in claim 11 and further characterized by this: that the extension of said mast, the cylinder of the first named ram, and the plunger of said second ram are all rigidly connected so as to move together as a single integrated unit.

13. A hydraulic lift-truck comprising a truck body, a mast having a main portion and an extension movable longitudinally on the main portion, a load-carrier movable longitudinally on said extension, a ram carried by and movable with said extension and the plunger of which is operatively related to the load-carrier to lift the latter on said extension, a second ram supported on the main portion of said mast and the plunger of which is operatively related to said extension to elevate the latter on the main portion of said mast, a reservoir, a conduit connecting the reservoir with the cylinder of said second ram, and a conduit connecting said cylinder with the cylinder of the other ram, and characterized by this: that the conduit connecting said cylinders passes through the plunger of said second ram, and that the extension of said mast, the cylinder of the first named ram, and the plunger of said second ram are rigidly connected together so as tomove as a single integrated unit.

WILBERT M. GILMAN.

REFERENCES CITED The following references are of record in the file of this patent:

V UNITED STATES PATENTS Number 

